Over the last few decades, the medical profession has widely considered that persons who exercise regularly experience better health over their lifetimes than sedentary persons. Exercise stretches and contracts muscles and stimulates breathing thereby improving blood circulation and lung function. Exercise has also been shown to improve insulin sensitivity for healthy persons and those with non-insulin dependent diabetes. Weight-bearing exercises also strengthen bones and may help decrease the risk of osteoporotic fractures.
However, when performed improperly, certain exercises may be harmful to a person. For example, when lifting weights, twisting and turning while lifting can lead to injury, such as a herniated disk and a lifetime of back pain. In fact, non-optimal usage of this equipment may restrict future motion due to a lack of full extension of muscles and supporting muscular skeletal systems. In order to ensure that an exercise regimen is performed properly, a person may hire a trainer to watch the exercises being conducted and correct deviations in proper form. However, in many situations, reliance on a trainer is costly and inconvenient as it requires a person's exercise regimen to also comply with the trainer's schedule. The same issues are also present for person's practicing a sports activity, where personal coaches are hired to improve form and effectiveness in the use of certain sporting equipment such as tennis rackets, golf clubs and the like.